(1) Field of the Invention
The present invention relates to a ventilation fan for use in a building; particularly, factories and agricultural buildings. In particular, the present invention relates to a ventilation fan having a backdraft assembly and providing minimal airflow resistance and increased efficiency.
(2) Description of the Related Art
The related art has shown various types of propeller blades. Illustrative are U.S. Pat. No. 3,169,694 to Borchers; U.S. Pat. No. 3,447,741 to Havette et al and U.S. Pat. No. 4,411,598 to Okada.
Borchers describes a propeller used for the movement of fluids such as in an axial flow fan. The propeller blade is shaped and positioned such that when the fan is running at a definite speed, the created vortex is projected with a centrifugal force at its periphery approximately equal to the static force of the ambient air.
Havette et al describes a faired propeller having a diffuser.
Okada relates to the vane structure of the fan, wheel rotor of a fluid propeller fan which provides a compromise between an axial flow fan and a centrifugal fan. The fan wheel assembly includes a wheel hub having a plurality of vanes extending radially from the wheel hub with each vane having a pitch angle which gradually decreases toward the wheel hub. The pitch angles of each of the vanes are selected so that radially inner portions of the individual vanes are capable of providing drought flow characteristics of axial flow fans while radially outer portions of the vanes are capable of providing drought flow characteristics of centrifugal fans.
The related art has also shown various types of automatic shutter assemblies having a frame with shutter members pivotably mounted across the frame. Illustrative are U.S. Pat. No. 1,706,280 to Dyer; U.S. Pat. No. 2,594,944 to Lohman, Jr.; U.S. Pat. No. 3,350,996 to Rose; U.S. Pat. No. 3,826,179 to Alley and U.S. Pat. No. 4,263,842 to Moore.
In the Dyer reference, the shutter members are formed of rectangular sheet metal plates. The shutter members are provided with a weighted member disposed relative to the pivotal axis so that while the shutter members are in the closed position, the center of gravity of each of the shutter members is located outwardly beyond the pivotal axis thereof, with the result that the shutter members have a tendency to swing on their pivots in a direction to cause an inward movement of their lower edges. Thus, the lower edges of the shutter members are firmly pressed inwardly against the faces of the adjacent shutter members. When, however, the fan is started and the air currents impinge upon the rear faces of the shutter members causing the shutter members to swing outwardly upon their pivots to a substantially horizontal position. The resistance of the shutter members to the air pressure during this movement is gradually decreased because of the fact that the center of gravity of each of the weighted shutter members moves gradually toward the vertical plane of its pivotal axis. When the shutter members are in their wide open positions, there is only a slight tendency of the shutter members to close, and very little air pressure is required to keep the shutter members in their wide open positions.
In the Lohman reference, the hinge ears of the carrier brackets for the shutter members counterbalances the major part of the weight of the forwardly extending free end portions of the shutter members and their interconnecting lever arms and tie bar. The counterbalance is calculated so that the shutter members will tend to move to the closed position under gravity yet will open quickly and easily when airflow pressure is directed against their inner faces. The shutter is also provided with a spring member to prevent the shutter members from remaining in the open position.
In the Rose reference, the shutter members are inverted, V-shaped members with inwardly directed arms preferably secured to each end of each blade and are pivotably connected to the sides of the frame by pivot members. A control member is connected to the arms and allows for manually adjusting the shutter members.
Alley and Moore show backdraft assemblies having airfoil shaped shutter members.
Of some interest is U.S. Pat. No. 3,072,041 to Downing which shows a shutter device having shutter plates located between the housing of the motor and the outer ring.
Also of interest are U.S. Pat. No. 3,335,654 to Killam; U.S. Pat. No. 5,215,438 to Chou et al and U.S. Pat. No. 5,547,339 to Burgers.
Killam shows a ventilating apparatus having an inlet for moving air into the centrifugal blower wheel. When the blower wheel is motionless, the outlet is closed by a flat swingable damper vane. The damper vane prevents outside drafts from traveling back through the wheel into the building.
Chou et al describes a self-centered orifice housing for an axial flow fan. The housing includes fan motor supports that also function collectively as a fan stator. The construction of the housing is such that assembling the motor into the housing results in the motor shaft being precisely located at the center of the housing orifice, so that there is a very small clearance between the orifice wall and blade tips of the fan. The inlet of the orifice is elliptical in cross-section. This configuration promotes attached flow in the air entering the orifice contributing to reduced noise generation and increased efficiency in the fan and orifice system.
Burgers describes a turbulator for a fluid impelling device such as an axial or centrifugal fan. The turbulator has a triangular cross-section and prevents flow separation as the fluid flow enters the inlet passage to decrease the acoustic level.
There remains the need for a ventilation fan having a square inlet which does not disrupt airflow into the fan and having a propeller which produces airflow having a constant velocity along the length of the blades to produce better airflow and also having an automatic backdraft assembly which is easily installed and removed.